U.S. law enforcement officials have devised an aggressive and potentially controversial new strategy to crack down on the illegal gun trade to Mexico by targeting cartel networks inside this country and "corrupt" U.S. firearms dealers, according to internal Justice Department documents obtained by NBC News.

The documents also state that the drug traffickers appear to have expanded efforts to acquire firepower in the U.S. by tapping well-developed supply networks beyond the Southwest border region in order to acquire high-powered assault rifles as well as components for improvised explosive devices (IEDs).

The new strategy was prepared in recent weeks by the Bureau of Alcohol, Tobacco and Firearms (ATF)’s Office of Field Operations, in the wake of stinging criticism of current ATF efforts to stem the flow of weapons to the cartels by the Justice Department’s inspector general.

Labeled “law enforcement sensitive,” it calls for ATF agents to put more emphasis on monitoring the activities of U.S. guns stores and other federally licensed firearms dealers who may be assisting or turning a blind eye to gun purchases by drug cartel operatives. The report describes such “corrupt” U.S. firearms dealers as “high value targets” -- a phrase that could rile gun rights groups and their supporters in Congress who charge ATF is already too aggressive in regulating the firearms industry.

The principal thrust of the revised strategy directs that ATF agents focus on taking down the operations of high-level gun traffickers working for specific Mexican cartels rather than simply trying to arrest low-level “straw buyers,” as they have often done in the past. It also calls on agents to use more sophisticated investigative methods, such as analyzing financial and telephone records, routinely used in terrorism and organized crime cases, and to work more closely with other federal agencies such as the Drug Enforcement Administration.

The new strategy document, entitled “Project Gunrunner; A Cartel Focused Strategy,” appears designed in part to address criticisms of enforcement efforts contained in a recently circulated draft report by the Justice Department’s Office of Inspector General. That report reviewed the efforts of Gunrunner, an ATF initiative that involves dispatching teams of agents known as Gunrunner Impact Teams (or GRITs) to cities near the border that are believed to be primary sources of weapons for the cartels.

But, as disclosed this week by NBC News, Justice Department investigators found that Gunrunner was riddled with “significant weaknesses,” including interagency turf fights, failures to share intelligence and a misguided investigative strategy that focused on low-level street buyers rather than the sophisticated criminal organizations employing them.

Some U.S. national security officials believe that the drug-related violence in Mexico is getting increasingly dire. Secretary of State Hillary Clinton, recently suggested the threat from Mexico’s drug cartels was beginning to resemble “an insurgency. In a Sept. 8 internal memo accompanying the new strategy, Mark Chait, ATF’s assistant director for field operations, wrote that “perhaps at no time our history has the investigation of firearms trafficking schemes and networks been more important to public safety, and increasingly, to national security, than now.”

But critics, especially gun-control groups, charge the Obama White House has paid insufficient attention to the problem, backing off from any efforts to tighten U.S. gun laws or even take basic steps such as nominating a director for ATF, the agency that is charged with policing the illegal weapons trade. ATF is currently being run by a deputy director, Kenneth Melson, a former federal prosecutor who critics – including many current and former ATF officials -- complain lacks the stature or clout to advocate for the agency’s interests inside the administration or solve its internal problems that are hindering firearms enforcement.

In just the last few months, law enforcement officials tell NBC, there have been alarming new signs that Mexican drug cartels and other Central and South American criminal organizations have been stepping up weapons purchases in the U.S. When ATF recently dispatched a GRIT team to Phoenix, it seized within a 100 days 1,300 illegally trafficked firearms and 71,000 rounds of ammunition, most of which were believed to have been bound to Mexico.

More significant, ATF recently identified more than 90 percent of the 158 semi-automatic assault rifles seized in May at a “narco training camp” run by Los Zetas, one of the most ruthless of the Mexican cartels, as coming from the United States. Only 13 of the weapons came from Central America, one senior law enforcement official said.

After that seizure, ATF traced a dozen of the assault rifles to a single firearms dealer operating out of his home in Henderson, Nev. On March 29, the dealer had sold the assault rifles to a Mexican national who had worked at a Las Vegas area Jack in the Box. The buyer purchased them for cash under a phony name, using a doctored driver’s license borrowed from a former co worker at the restaurant, according to Tom Chittum, the resident agent in charge of ATF’s Las Vegas office. Just 38 days later, the same high-powered assault rifles were at the Zetas training camp in Higueras, Mexico, 70 miles south of the U.S. border, he said.

The weapons “were purchased with the intent of supplying the (drug) traffickers in Mexico -- I don’t think there’s any dispute about that,” said Chittum. The Mexican national, his father and his brother have all been charged with illegal weapons purchases in the case. No charges have been filed against the firearms dealer and he is not accused of any wrongdoing.

The new strategy document lays out the dimensions of the problem in stark terms. While shying away from specific figures -- which have been the source of fierce debate -- it concludes that “a significant percentage” of all the weapons seized from the Mexican cartels are originating in the U.S.

Just as worrisome, it cites evidence that the cartels are tapping into the U.S. market to buy components for improvised explosive devices or IEDs, the same type of sophisticated bombs that have been used against U.S. troops in Iraq and Afghanistan. A senior law enforcement official said that some ATF agents “rang the bell” about the prospect of IEDs being used by the Mexican cartels over a year ago, when they first saw reports of the thefts of commercial explosives near the Southwest border. .

The ATF strategy document cites intelligence that the cartels have specifically “tasked” their money laundering, drug distribution and transportation “infrastructures” with “reaching into the United States” to acquire firearms, ammunition and components to construct IEDs. It concludes that three cartels in particular are responsible for most of the purchases -- the Gulf and Sinoloa cartels and Los Zetas, a cartel founded by rogue Mexican military officers.

The strategy appears to accept many of the criticisms in the Justice Department inspector general’s report, especially the ATF’s past emphasis on targeting low-level “straw buyers” hired by cartel operatives to buy weapons at U.S. gun stores. It notes that straw purchasers are easily replaced and often are selected by higher level traffickers because they have no serious criminal records, making them undesirable candidates for prosecution.

“Straw purchasers must be held accountable for their conduct and made ineligible to purchase or possess firearms in the future,” the report states. “However, straw purchasers should more frequently be viewed as persons whose conduct should be investigated as part of a larger conspiracy and as persons whose information, cooperation and assistance should be exposed to the extent possible in further of the ultimate goal of identifying key members of the trafficking enterprise.”

It also calls for ATF agents to work more closely with other federal agencies, particularly the Organized Crime Drug Enforcement Task Force (OCDETF) run by local U.S. Attorney’s offices and involving all federal law enforcement agencies. The draft inspector general report had sharply criticized ATF agents for not sharing intelligence and working more cooperatively with other federal agencies, especially the Bureau of Immigration and Customs Enforcement (ICE.)